1. Field of the Invention
This invention relates generally to variable displacement piston pumps and, particularly, to pumps of the type described which are compensated for maintaining constant pressure with variable flow. More particularly, this invention relates the hydrostatic means for controlling the stroke of the pump pistons to provide the aforenoted compensation.
2. Description of the Prior Art
The pump disclosed is particularly intended for use in electronic actuator diesel fuel injection systems. For this application and for other applications, a minimal pressure ripple or variation with a variation in fluid flow is desirable. Check valve type pumps, which are well known in the art, fulfill this requirement by including check valves for controlling pump discharge and/or inlet functions, and further include an arrangement for varying the stroke of the pump pistons. In pumps of this type, the pressure in the piston cylinders must be slightly greater than the pressure in the discharge manifold before the check valve opens. This is contrary to rotating cylinder block type pumps wherein communication is established between the cylinders and the discharge manifold at some predetermined pump shaft angle, without regard to the respective pressures. The pump disclosed in aforenoted U.S. application Ser. No. 796,933 features an arrangement affected by pump discharge manifold pressure for transmitting a thrust load to vary the stroke of the pump pistons. The arrangement disclosed requires relatively expensive thrust bearing. The present invention uses a less expensive hydrostatic bearing arrangement for this purpose.